The long-term objective of our research is to understand the molecular mechanisms of cell death as a consequence of harmful environmental conditions. There appear to be several distinct circumstances under which cell death takes place in multicellular organisms. For example, apoptosis (programmed cell death) is known to play an important role in embryonic development, normal cell turnover, and hormone-dependent atrophy. Environmentally adverse chemicals can lead to cytotoxicity and, ultimately, cell death. Although apoptosis and cytotoxicity appear to occur for many reasons and respond to a variety of signals, it has become increasingly evident that there exist common steps in the pathways leading to cell death. Chemicals causing oxidative damage are metabolized by "Phase I" (oxygenation) and "Phase II" (conjugate) enzymes. We propose to use the aromatic hydrocarbon-responsive [Ah] gene battery as a model system for studying the cellular response of protection against oxidative stress and cell death. In the mouse, the [Ah] battery comprises at least six genes: two Phase I genes, Cypla1 and Cypla2; and four Phase II genes, Nmo-1, Aldh- 1, Ugt-1 and Gt-1. The radiation-induced deletion homozygote c14CoS/c14CoS mouse (albino phenotype) is missing about 1 centiMorgan of chromosome 7, dies during the first 18 h post partum, and exhibits marked activation of the Nmo-1 gene, increases in Aldh-1 mRNA, and elevated Ugt-1 and Gt-1 enzyme activities. Interestingly, in the 14CoS/14CoS fetus and newborn, three growth arrest- and DNA damage-inducible (gadd) genes are also activated. We postulate that the region of mouse chromosome 7 missing in the 14CoS/14CoS mouse contains a "master switch" gene, which we have designated Nmo-1n, encoding a trans-acting factors(s) that is a negative effector of the Nmo-1 gene. Under normal conditions, Nmo-1n suppresses an unknown number of genes. In response to environmental adversity such as oxidative stress, this gene releases its negative control on the [Ah] battery Phase II genes, and perhaps the gadd genes, thereby allowing all of these genes it become expressed. This response is independent of Phase I (Cypla1 and Cypla2) gene expression. Whether this region on chromosome 7 represents a single gene, Nmo-1a, controlling both the [Ah] battery Phase II genes and the gadd genes, or whether there are two or more gene controlling the [Ah] battery Phase II genes and the gadd genes, will require further work. Our first goal is to clone, sequence and characterize by functional analysis the murine Nmo-1 and Aldh-1 genes and regulatory regions. We then propose to use this information for cloning and characterizing the murine Nmo-1n gene. Knowledge about the Nmo-1n gene and its product will surely help clarify the functional relevance of common pathways involved in protection against oxidative damage and cell death.